1. Field of the Invention
This invention relates to serial port technology. More particularly, it relates to a converting apparatus for transferring data between DCE and DTE through a universal serial bus (USB) and its control method.
2. Description of the Prior Art
Three drawbacks top any list of the most aggravating aspects of conventional RS-232C serial ports: low speed, complex cabling, and the limited number of ports. First introduced in 1996, the Universal Serial Bus (USB hereinafter), solves all three. It combines a signaling rate of 12 Mbits/sec with a mistake proof wiring system, allows the connection of up to 127 peripheral devices, has low cost and plug-and-play functions. In other words, it is much more than a successor to the RS-232C serial port. At present, several USB functions such as displays, keyboards, mice, joysticks, scanners, etc., have been successively realized by USB's vendors. However, since a common protocol has not been established in conventional communication equipment (such as instrument control interface, data acquisition equipment, modem, telephones, integrated service digital network terminal adapter (ISDN TA), etc.), the universal asynchronous receiver/transmitter (UART) currently prevails in asynchronous serial reception/transmission.
Referring to FIG. 1, a diagram illustrates the connection between a data terminal equipment (DTE) 1 and a data communications equipment (DCE) 2 of the prior art. Generally, the DTE 1 refers to a computer console, and the DCE 2 refers to an instrument control interface, data acquisition equipment, modem, telephones and integrated service digital network terminal adapter among others. In general, the DCE 1 as used here refers broadly to the equipment for asynchronous serial reception/transmission. In the drawing, an RS-232C cable 10 is coupled between the DTE 1 and the DCE 2, whose two ends 12 and 14 connected to the DTE 1 and the DCE 2, respectively, are all RS-232 connectors. The DTE 1 has an internal UART chip 16 (commonly known as 16450 or 16550) serving as an interface between the DTE 1 and DCE 2 for asynchronous serial reception/transmission.
Therefore, a converting device is required for transferring the asynchronous serial signals through a USB of the DTE 1 to and from the DTE 2, enabling the asynchronous serial reception/transmission equipment to work with the USB interface before or even after a communication protocol prevails.